The invention relates to an electrically powered coolant pump in accordance with the preamble of claim 1.
Electrically powered coolant pumps are increasingly employed as drive elements for the cooling water circuit of an internal combustion engine in an automotive vehicle. In comparison with a pump of a conventional construction type which is coupled with the engine speed, these have the advantage of being able to convey cooling water independently of the engine speed and are thus, for example, also capable of conveying at standstill. One example for such a coolant pump is described in DE 296 18 558 U1. This pump has the form of a centrifugal pump whereby the coolant entering in an axial direction is radially deflected into a volute outlet passage and conveyed back into the internal combustion engine. The function of drive mechanism for the impeller of the centrifugal pump is in this example served by an electric motor flange-mounted to the internal combustion engine, which includes a stator and a rotor mounted therein on a hollow shaft. Between the rotor and the stator there is a shroud surrounded by cooling water. The electric motor or the shroud, respectively, is therefore located off the direction of flow of the coolant.
This design of a coolant pump does, however, present drawbacks: Thus the maximum rotational speed of the like wet-rotor pumps is generally limited to approx. 4,500 rpm so as to still be able to keep power losses low, in particular those due to the drag losses which steeply increase with the rotational speed.
In order to nevertheless be capable of providing the desired capacity, these known electrical coolant pumps therefore have correspondingly large dimensions. In addition, for the very reason of its design with a radially acting impeller, this coolant pump requires a considerable structural space so that the coolant may be deflected in a desired manner without excessively high friction losses occurring. The locations suited for installation of a coolant pump of this type are accordingly very limited, particularly in the engine room of an automotive vehicle. Particularly in the case of such an application the comparatively high weight of this design is moreover found to be a drawback, for here any additional weight units have a negative effect on consumption of the internal combustion engine. Traditionally a power-to-weight ratio of, e.g., approx. 1.1 kg/100 W is given.
The invention is therefore based on the object of further developing a coolant pump in accordance with the preamble of claim 1 in such a way that it allows for a high degree of liberty as regards the installation location, at low weight and a smaller demand for structural space.
This object is attained through an electrically powered coolant pump having the features of claim 1.
Thus in accordance with the invention it was particularly provided that the pump housing has an elongate shape and on the inlet side encloses the pump wheel and downstream therefrom encloses the electric motor, with an annular flow passage for the coolant being arranged between the pump housing and the outside of the electric motor, and with the electric motor being encapsulated against the coolant. This has the essential advantage that the coolant flows over the electric motor, as well, and very effective cooling of the electric motor is possible thanks to the large heat exchange area. The electric motor is retained in the pump housing with the aid of at least one web so that it may be driven.
In particular it was recognized in accordance with the invention that the losses of a pump generally increase at the fifth power of the wheel diameter. At the same time, however, the losses only increase at the third power of the rotational speed, for which reason the electric pump of the invention is designed so as to predominantly derive its power from rotational speed, i.e., it aims for higher rotational speeds than the prior art.
Other than in the prior art where the theoretical maximum rotational speed of the utilized pumps cannot be exploited for the named reasons, in accordance with the invention the entire performance spectrum of the electric motor can be utilized thanks to its arrangement in the coolant flow. Where maximum rotational speeds of approx . . . 4,500 rpm were still attainable in the prior art, rotational speeds of more than 12,000 rpm and in particular 15,000 rpm may for the first time also be attained with the electric pump of the invention.
The permanent water cooling of the electric motor""s coil jacket obtained in accordance with the invention, and thus carrying off the heat losses of the electric motor through the steady flow of the coolant over the external shell of the motor, permits to obtain an optimized degree of usefulness. As a result, very high performances may be attained with a relatively small-sized motor.
This increased efficiency in comparison with the prior art moreover brings about a drastic improvement of the power-to-weight ratio to, e.g., approximately 350 g/100 W, which has a particularly advantageous effect with regard to the weight of the assembly.
At the same time, the electric motor as well as an optionally associated electronic control circuitry may be provided at very low cost.
On account of the high rotational speeds that are possible, the diameter of the pump wheel may moreover be kept small, so that the resulting losses may be reduced. At the same time this also allows for a substantially smaller size of the coolant pump of the invention in comparison with the prior art, thus expanding the possibilities of installation in an engine room etc. As the pump according to the invention moreover is designed as a so-called xe2x80x9cinline pumpxe2x80x9d, it may particularly well be integrated into cooling circuits and is of extraordinarily universal use.
Although fuel delivery pumps in the form of xe2x80x9cinline pumpsxe2x80x9d are also known in the field of automotive vehicles, in these the fuel flows through the magnet gap over the commutator of the electric motor, which makes them wet-rotor pumps. The maximum rotational speed of the electric motor is limited in fuel delivery pumps of this type because the drag losses strongly increase at elevated rotational speeds. These known fuel delivery pumps are designed with a view to applying high pressures on the fuel at relatively low rotational speeds. A dry-rotor motor may not enter into consideration here, for possibly occurring leakages into the hot rotor cavity might result in explosion.
In contrast, the present invention provides to furnish a coolant pump whereby large flow quantities may be conveyed at high rotational speeds, something that is not possible with the known fuel delivery pumps.
Advantageous developments of the invention result from the features of the subclaims.
Thus the electric motor may be followed downstream by an electronic control unit for driving the electric motor. As a result, it is advantageously possible to also obtainxe2x80x94besides a very compact designxe2x80x94permanent cooling of the electronic control unit through the coolant flowing past. The capacity of the coolant pump in accordance with the invention may therefore be further increased while the required installation space is decreased.
It is moreover also possible for the electronic control unit to include a metallic support member, the particularly good heat conductivity of which permits good discharge of the heat energy generated by the electronic components into the coolant.
It is furthermore advantageous if the pump wheel is an axial pump wheel. These allow for particularly high rotational speeds, so that the actual capacity of the electric motor, cooled by the coolant flowing through it in accordance with the invention, may be utilized particularly well.
As an alternative it is also possible for the pump wheel to be designed as a semiaxial pump wheel which is advantageous in particular applications, for example when it is necessary to overcome greater pumping heads.
If the external diameter of the pump wheel substantially corresponds to the internal diameter of a supply conduit to the pump housing, a smallest possible impeller diameter may be achieved. This makes particularly advantageous use of the high rotational speeds of the pump wheel, whereby high flow rates are made possible even at such small cross-sections of flow. At the same time an extremely small size may be obtained for the coolant pump according to the invention.
It is of further advantage if the cross-sectional area of flow of the annular flow passage around the electric motor is adapted to the cross-sectional area of the flow inlet opening, for in this way friction or pressure losses within the coolant pump may be kept minimum. Hereby even better efficiency of the assembly may be attained.
If the first bearing of a shaft supporting the pump wheel is arranged in the vicinity of the pump wheel, the latter may be mounted particularly well with a view to the high rotational speeds, so that the dynamic loads at the pump wheel are low. Moreover the first bearing may therefore also be designed to have relatively small dimensions, which reduces friction losses and increases the overall efficiency of the coolant pump.
Herein the first bearing may in particular have the form of a slide bearing, which has the result of very reliable and durable mounting even if this bearing is arranged within the coolant.
As an alternative it is also possible for the first bearing to have the form of a rolling bearing, whereby particularly low friction may be achieved at this bearing. Sealing of this rolling bearing against the coolant may, for example, be achieved by means of a shaft seal ring or the like.
It is of particular advantage if the first bearing has a geometrical relation with the impeller housing. Through the possibility of processing bearing diameter and housing diameter in a chucking fixture, a minimum xe2x80x9cairxe2x80x9d gap at the impeller external diameter of, e.g., approx. 0.02 mm may be adjusted.
Moreover a second bearing of a shaft supporting the pump wheel may be arranged on the electric motor, wherebyxe2x80x94besides a compact designxe2x80x94a reliable support against the dynamic loads owing to the pump wheel may be achieved.
The second bearing may have the form of a rolling bearing and be encapsulated against the coolant, whereby mounting is particularly reliable even at the aspired high rotational speeds and low friction losses may be achieved. A detrimental influence of the coolant on the bearing by is moreover effectively precluded by its encapsulation against the coolant, which has a positive effect on the life time of the bearing. As a rolling bearing, in particular a deep groove ball bearing may be used which is also suited for receiving axial forces.
It is of further advantage if the second bearing is encapsulated against the coolant by means of a shaft seal ring. Such shaft seal rings have variously also been found under practical conditions to be very reliable even at high rotational speeds. It is therefore possible to revert to time-tested and economic measures for encapsulation of the second bearing.
The shaft may moreover be formed in two parts and comprise a corrosion-proof needle pin and a shaft portion, wherein the needle pin serves as a sliding partner for the shaft seal ring and is press-fitted into the shaft portion, and wherein the needle pin consists of a material that has a higher hardness than the material of the shaft portion. Through the combination of a hard material for the needle pin and a softer material for the shaft portion, a reliable and durable combination of these shaft components may be obtained. In addition the material properties at a respective shaft portion may individually be adapted to the respective sliding partner. Hereby the reliability and functionality of the coolant pump in accordance with the invention may be further improved.
If the at least one web is formed of an elastomer synthetic material, acoustic decoupling of the electric motor from the pump housing may be achieved, which contributes to noise attenuation. At the same time an improved thermal insulation against the pump housing is achieved.
The structural component of electric motor and pump wheel may moreover be retained in the pump housing by a plurality of webs distributed over the circumference, resulting in a very reliable and compact design for the coolant pump.
It is moreover an advantage if the pump wheel is formed of a flexible and impact resistant synthetic material as this permits elastic yielding of the pump wheel in the event of particles being present in the pump wheel gap. Blocking of the pump wheel may thus be avoided even more reliably. In practical testing PEEK was for example found to be a particularly suitable material.
As an alternative, or in addition, the supply conduit to the pump housing which encloses the pump wheel may also be formed of a synthetic material which is capable of embedding particles to thus prevent blocking of the pump wheel. For this purpose preferably a relatively soft synthetic material is used, so that the particles may retreat into it and damage to the pump wheel will not occur.